Breast cancer is the second leading cause of death among women. Little is known about the influence that diagnosis and treatment for cancer has on family members, particularly sisters. The present study seeks to determine whether t6he diagnosis of cancer in a woman will increase the cancer screening and preventive behavior among her unaffected sisters. In this study we will recruit 500 sisters of newly diagnosed breast cancer cases to conduct a study of cancer screening behavior. These sisters will be recrutied via family practice physicians and through hospital tumor registries. Unaffected sisters will be mailed a qiuestionnaire to measure cancer screening behaviors in three categories: physician breast exam, BBSE, and mammography. Cancer risk behaviors such as smoking, drinking alcohol, as well as potential risk factors such as dietary fat, will also be measured Baseline data will be analyzed to determine the level of cancer screening and the influence of the sister's cancer on perceptions of risk and actual screening. These data will be compared with national population data collected during 1978-1988 by the National Cancer Institute. We will test a mass mailed intervention to encouage screening behavior consistent with the NCI and ACS guidelines. Sisters will be stratified by method of recruitment and then semi-randomly assigned to an intervention or a control group based on birth day, with all sisters of a case assigned to the same condition. Data from the baseline survey will be used to verify that the assignment procedures yield equivalent intervention and control groups. Sister will be measured one year after the intervention time period. We will make experimental comparisons between the intervention and control groups and we will test for interactions between certain covariates (such as age) and intervention effects. We will test the feasibilty of a dissemination strategy designed to reach women at elevated risk. Feasibility will be assessed on the basis of physician participation rates, breast cancer case referral rates, and ease of recruitment of sisters of breast cancer cases